from what we can see in the APEX debug output you've posted, the validation fails when using APEX Listener, because the file name doesn't seem to be transmitted.
Could you provide some additional information on your setup? APEX version seems to be 4.1 from what I can see in your log, but which APEX Listener version do you use on which JEE Container (if not running APEX Listener in Standalone Mode), and which Database version is the home for your APEX?
The blog post you've referenced contains a step that seems to be incomplete. It says

I was interested to test the new Excel upload feature, to get to work I added following line to the config file (apache-tomcat/temp/apex/apex-config.xml)

true

I don't know if this is a temporary error on that page, but it indicates you've perhaps made changes to apex-config.xml and possibly to web.xml due to other configuration task as well. Can you please describe what kind of changes you've implemented to configure your APEX Listener?

Last, but not least: Do you receive any error in the APEX Listeners log for that action?
Is your web server running on the same machine you run your APEX Listener on? If so, did you configure a different port for APEX Listener?